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Biomedical subjects

W E Caler

Publications and source records attributed to W E Caler.

13 recordsLinked to original sources
PubMed1996

In vitro stimulation of articular chondrocyte mRNA and extracellular matrix synthesis by hydrostatic pressure.

This study tested the effects of hydrostatic pressure (10 MPa) on adult articular chondrocyte mRNA and extracellular matrix synthesis in vitro. High density primary cultures of bovine chondrocytes were exposed to hydrostatic pressure applied intermittently at 1 Hz or constantly for 4 hours in serum-free medium or in medium containing 1% fetal bovine serum. mRNAs for aggrecan, types I and II collagen, and beta-actin were analyzed by Northern blots and quantified by slot blots. Proteoglycan synthesis was quantified by 35SO4 uptake into cetylpyridinium chloride-precipitable glycosaminoglycans, and cell-associated aggrecan and type-II collagen were detected by immunohistochemical techniques. In serum-free medium, intermittent pressure increased aggrecan mRNA signal by 14% and constant pressure decreased type-II collagen mRNA signal by 16% (p < 0.05). In the presence of 1% fetal bovine serum, intermittent pressure increased aggrecan and type-II collagen mRNA signals by 31% (p < 0.01) and 36% (p < 0.001), respectively, whereas constant pressure had no effect on either mRNA. Intermittent and constant pressure stimulated glycosaminoglycan synthesis 65% (p < 0.001) and 32% (p < 0.05), respectively. Immunohistochemical detection of cell-associated aggrecan and type-II collagen was increased in response to both intermittent and constant pressure. These data support the hypothesis that physiologic hydrostatic pressure directly influences the extracellular matrix metabolism of articular chondrocytes.

Aggrecans↗
PubMed1996

Cyclic mechanical property degradation during fatigue loading of cortical bone.

Fatigue damage accumulation has been demonstrated in living bone and postulated as a stimulus to the bone modeling and remodeling response. Mechanical property degradation is one manifestation of fatigue damage accumulation. This study examines changes in secant modulus and cyclic energy dissipation behavior during axial load-controlled fatigue loading of cortical bone specimens. The findings suggest that secant modulus degradation and cyclic energy dissipation are greatly increased at loading levels above critical damage strain thresholds of 2500 and 4000 mu epsilon in tensile and compressive fatigue, respectively. Tensile and compressive fatigue loading also caused different forms of modulus degradation at loading levels above these thresholds. Bone behaves as a linear viscoelastic material below these thresholds, even after prior property degradation at higher loading levels. Cyclic energy dissipation was proportional to the 2.1 power of the applied effective strain range for all loadings below 2500 mu epsilon. Above 2500 mu epsilon, tensile fatigue loading caused cyclic energy dissipation proportional to the 5.8 power of the applied effective strain range. Compressive fatigue loading dissipated cyclic energy proportional to the 4.9 power of applied effective strain range over 4000 mu epsilon. Lifetime energy dissipation over all fatigue tests to fracture at a single loading level was well fitted by the same power law in the number of cycles to failure raised to the 0.6 power. Loading levels of 2500 mu epsilon in tension and 4000 mu epsilon in compression are within the ranges observed in living animals, and thus these phenomena may play a role in initiating the remodeling response in live bone tissue.

Adolescent↗
PubMed1992

A comparison of unicortical and bicortical end screw attachment of fracture fixation plates.

Plate fixation is considered by many clinicians to be the treatment of choice for displaced diaphyseal fractures of the forearm. One possible complication associated with plate fixation is refracture with the plate in situ or after plate removal. With the plate in situ, refracture typically occurs through the last screw hole near the end of the plate. Some clinicians have advocated the use of unicortical end screws to minimize the risk of such refractures. In this study, we performed a series of in vitro tests to compare the breaking strength of plated bone analogues that used either unicortical or bicortical end screws. The plated constructs that used unicortical end screws were significantly weaker in the two most important physiologic loading modes. Based on these results, we conclude that the use of unicortical end screws may result in a greater risk of refracture with the plate in situ.

Bone Plates↗
PubMed1989

Bone creep-fatigue damage accumulation.

Creep and fatigue tests were performed on human femoral cortical bone and the results were compared to a cumulative damage model for bone fracture. Fatigue tests in tension, compression, and reversed loading with a tensile mean stress were conducted at 2 Hz and 0.02 Hz. Load frequency had a strong influence on the number of cycles to failure but did not influence the total time to failure. Bone displayed poor creep-fracture properties in both tension and compression. The fracture surfaces of the tensile creep specimens are distinctly different than those of the compressive specimens. The results suggest that tensile cyclic loading creates primarily time-dependent damage and compressive cyclic loading creates primarily cycle-dependent damage. However, data for load histories involving both tensile and compressive loading indicate lower time to failure than predicted by a simple summation of time-dependent and cycle-dependent damage.

Adult↗
PubMed1988

A biomechanical assessment of plate fixation, with insufficient bony support.

The use of an internal fixation plate in the presence of a bone defect was studied using a theoretical model of an idealized long bone having a circular cross section and loaded using a combination of axial and bending loads. The analysis showed that the "bending-open" loading mode does not occur if, in the normal unplated bone, the line of action of the resultant axial load passes within the outer cortex at the location where the plate is to be applied. In this situation the fracture will deform in a "bending-closed" mode regardless of whether the plate is attached to the tension or the compression side. If bony contact cannot be achieved, lower plate stress is always encountered when the plate is attached to the compression side instead of the tension side. In vivo verification of the model was addressed in a pilot experiment using instrumented metal plates applied bilaterally to the femora of one dog. Bilateral bone defects were created in the midfemoral canine diaphysis. On one leg the plate was applied to the lateral aspect ("tension" side), and on the other leg the plate was applied to the medial aspect ("compression" side). The plate attached to the lateral aspect deformed plastically in the bending-closed mode. The contralateral plate that was attached to the medial aspect (compression side) of the femur did not show signs of plastic deformation. Furthermore, the plate strains were lower in the plate attached to the medial aspect than those in the plate attached to the lateral aspect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

A cumulative damage model for bone fracture.

A mathematical model is presented to describe the combined time-dependent and cycle-dependent fracture characteristics of devitalized cortical bone. Failure is interpreted based on a linear-life fraction rule, which accounts for cumulative creep and fatigue damage under arbitrary loading histories. The model is successful in describing the influence of loading rate on monotonic tensile strength, the time to failure in constant stress creep-fracture tests, and bone fracture in zero-tension and tension-compression cyclic loading. The possible implications of the model to in vivo bone fracture, deformity, and remodelling in response to various loading histories are considered.

Adult↗
PubMed1985

Long bone torsion: II. A combined experimental and computational method for determining an effective shear modulus.

A technique is established which allows an effective torsional shear modulus to be determined for long bones, while remaining nondestructive to whole bone specimens. Strain gages are bonded to the diaphysis of the bone. Strains are then recorded under pure torsional loads. Theoretical stress predictions are combined with experimental strain recordings to arrive at a modulus value. Shear modulus calculations for four canine radii are reported using theoretical stress predictions from circular, elliptical and finite element models of the transverse bone geometry. The effective shear modulus, obtained from an average of the shear moduli determined at strain gage locations, serves to average the heterogeneous shear modulus distribution over the cross section. The shear modulus obtained is that associated with the "circumferential" direction in transverse planes.

Animals↗
PubMed1984

Changes in long-bone structural properties during the first 8 weeks of plate implantation.

The midplate structural rigidities of metal- and plastic-plated intact canine femora were experimentally determined after initial plate application and 8 weeks after in vivo implantation. Composite beam theory significantly overestimated the bending rigidities of the metal-plated bones. The rigidities of the plastic-plated bones were nearly identical to that of the isolated bone, as composite beam theory predicted. Plating with either plate increased the intracortical porosity and caused the deposition of periosteal new bone, which was greater with plastic than with metal plates. The increased rigidities provided by the attachment of the metal plates and, hence, the degree of bone strain shielding were variable. Platings for 8 weeks which provided little strain shielding with either metal or plastic plates caused an increase in bone flexural rigidity (measured after plate removal) with respect to the contralateral control. Platings that provided increasing amounts of strain shielding caused a decreasing midplate bone rigidity (measured after plate removal) and increasing bone deposition at the outer screws. These findings suggest that the surgical implantation of any plate (metal or plastic) will provide a net stimulus to bone formation and consequently increased bone structural rigidity, even though intracortical porosity is increased. If the plate significantly reduces the normal loads borne by the bone, however, there is a net stimulus to remove bone, resulting in a loss of midplate structural rigidity within 8 weeks of implantation.

Animals↗
PubMed1983

Cycle-dependent and time-dependent bone fracture with repeated loading.

Fatigue tests of human cortical bone (up to 1.74 X 10(6) cycles) were conducted under tension-compression (T-C) and zero-tension (O-T) modes with a 2Hz, stress controlled, sinusoidal loading history. Tensile creep-fracture tests at constant stress levels were also performed. The relationship between the initial cyclic strain range and cycles to failure with the T-C specimens were consistent with that derived previously in low-cycle fatigue under strain control. Using a time-dependent failure model, the creep-fracture data was found to be consistent with previous studies of the influence of strain rate on the monotonic tensile strength of bone. The model also predicted quite well the time to failure for the O-T fatigue specimens, suggesting that creep damage plays an important role in O-T fatigue specimens.

Adult↗
PubMed1981

Fatigue behavior of adult cortical bone: the influence of mean strain and strain range.

Uniaxial fatigue tests were conducted of devitalized cortical bone specimens machined from human femora. Specimens were tested at strain ranges from 0.005 to 0.010 under physiologic loading rates. The influence of compressive, zero, and tensile mean strains on fatigue life and on the stress/strain histories during fatigue were examined. Results showed that bone fatigue is a gradual damage process accompanied by a progressive increase in hysteresis and a loss of bone stiffness. The total number of cycles to fatigue failure was influenced only by the total strain range and was not affected by mean strain. Bone was shown to have extremely poor fatigue resistance. Fully reversed cyclic loading to one half of the yield strain caused fatigue fracture in 1000 cycles. Biological implications. The bone regions which experience the highest strain ranges in vivo generally have a compressive mean strain. The results of this study indicate that mechanical fatigue damage accumulates more rapidly in these "compressive" areas than in "tensile" areas of bone.

Aged↗